Subject: Re: bug#32672: 27.0.50; image resize on window resizing

From: martin rudalics <[email-masked]>
Date: Tue, 25 Sep 2018 09:26:47 +0200

>> As I said, redisplay would not have to care about that at all.  It
 >> would simply call 'window-state-change-functions' where it calls
 >> 'window-size-change-functions' now.  And running
 >> 'window-state-change-functions' would use one boolean set (among
 >> others) instead of where 'run-window-configuration-change-hook' gets
 >> called now and which it resets.  Iff that boolean was set, it would
 >> start to find all windows where a relevant change occurred and run the
 >> functions.  Buffer-locally iff a window shows the buffer for which the
 >> local hook was set and something changed for that window.
 >
 > Those functions will need to keep track of the changes, or record the
 > previous state attributes somewhere, to do their job, right?  Are you
 > saying that these are already recorded/tracked?  If not, they will
 > need to be added, which was the point I was making.

I'm not sure what you mean with "Those functions".  Running
'window-size-change-functions' already records the current sizes in
preparation for the call during next redisplay.
'window-state-change-functions' would do the same for the values it
manages.

 >> The great advantage for users and application programmers would be
 >> that their functions would run once only and only if something really
 >> changed since last redisplay.
 >
 > Even the "once" part might be problematic, because redisplay_internal
 > sometimes re-runs its code more than once, as you know.  The "really
 > changed since last redisplay" is even trickier, because a given
 > redisplay cycle doesn't always finish all of its job, it can stop in
 > the middle and return after doing only part of what needs to be done,
 > in which case some of the windows are not updated, and we will have
 > lost our point of reference.

What you mention here would affect 'window-size-change-functions'
already now.  I see no great harm in that.  If running
'window-size-change-functions' succeeds, callers will have adapted to
the new sizes and no further calls are necessary.  If it fails, the
old sizes will continue to exist and the functions will be called
(maybe again) during the next internal redisplay.

martin